MP3 is a digital music format which allows CD tracks to be reduced to around a tenth of their normal size without a significant loss of quality. MP3 gets rid of a lot of the information recorded in a song that our ears are not able to hear and then uses complex algorithms to reduce the file size. This then enables you to get hundreds of songs on to a CD and it also has opened up a new market over the internet - the download market as download times have been significantly reduced.
The MP3 format is a lossy format. That means that an MP3 file does not contain 100% of the original audio information. Instead, MP3 files use perceptual coding. In other words, that means it removes the information that your ear doesn't notice thereby making the file smaller. The reason lossy formats are used over RAW is that RAW audio files are too large to travel over the internet at any great speed. By using lossy formats it enables even dial up users to download mp3 files at a reasonable speed. RAW file formats generally require 176,000 bytes per second compared to a lossy format which requires 17,600. The difference is massive and so are the download times.
AC3 is an audio file specifically developed by Dolby Digital to provide surround sound audio. The format is used for audio on many DVD and Blu-Ray media. In order for the file to be correctly decoded and output, a DVD player with a Dolby Digital compatible home cinema system is required. It became the de facto standard for surround sound, and has held that position since its inception in 1992, with it coming to home cinema in 1995.
AC3 allows for separate audio to be defined for each of the 6 speakers in the standard cinema and home cinema setup. This produces the effect of surround sound to the person listening to the audio file. The six channels consist of right front, center, left front, rear right, rear left and a sub woofer.
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